<template>
  <ul class="list">
    <li class="item"
        v-for="item of letters"
        :key="item"
        :ref="item"
        @click="handleLetterClick"
        @touchstart="handleTouchStart"
        @touchmove="handleTouchMove"
        @touchend="handleTouchEnd"
    >
      {{item}}
    </li>
  </ul>
</template>

<script>
  export default {
    name: "CityAlphabet",
    props:{
      cities:Object
    },
    computed:{
      letters(){
        const letters=[]
        for(let i in this.cities){
          letters.push(i)
        }
        return letters
      }
    },
    data (){
      return{
        touchStatus:false,
        startY:0,
        timer:null
      }
    },
    updated (){
      this.startY=this.$refs['A'][0].offsetTop
    },
    methods:{
      handleLetterClick(e){
        this.$emit('change',e.target.innerText)
      },
      handleTouchStart (){
        this.touchStatus=true
      },
      handleTouchMove (e){
        if(this.timer){
          clearTimeout(this.timer)
        }
         this.timer=setTimeout(()=>{
           if(this.touchStatus){
             const touchY=e.touches[0].clientY-79
             const index=Math.floor((touchY-this.startY)/20)
             if(index >=0 && index < this.letters.length){
               this.$emit('change',this.letters[index])
             }
           }
         },16)
      },
      handleTouchEnd (){
        this.touchStatus=false
      },
    }
  }
</script>

<style scoped lang="stylus">
  @import '~styles/varibles.styl'
  .list
    display: flex
    flex-direction:column
    justify-content: center
    position: absolute
    right: 0
    top: 1.58rem
    width: .4rem
    bottom: 0
    .item
      line-height: .4rem
      text-align: center
      color: $bgColor
</style>
